1. Field of the Invention
This invention relates generally to ducting as used in air conditioning and heating systems, and more particularly to a duct fitting specifically contoured to be used with highly flexible ducting in a multi user system.
2. Description of the Prior Art
It is customary in the heating, cooling and ventilating field to use a main or trunk duct, having extending from it one or more branch ducts. Various fittings have been proposed for connecting a branch duct to an associated main duct. One manner of attaching a fitting to a duct is shown in U.S. Pat. No. 3,290,066 to Primich et al entitled "Sheet Metal Pipe Fitting," which issued Dec. 6, 1966. In that device, a plurality of tabs formed so as to extend axially from the fitting are to be bent over in order to secure the fitting on an associated duct. A significant problem, however, exists with regard to time, tools and the relatively high degree of skill required to accurately cut a properly sized hole in the trunk duct. Such a trunk duct may of course be constructed from rigid or from flexible material, such as reinforced fiberglass and the like. As will be seen hereinafter, the duct fitting forming the subject matter of this invention is primarily configured for use with highly flexible ducting, although it may also be utilized with certain diameter rigid ducting.
U.S. Pat. No. 3,349,792 issued to Larkin on Oct. 31, 1967, and U.S. Pat. No. 3,609,056 issued to Hougen on Sep. 28, 1971, disclose examples of hole cutting tools which can be used for cutting holes in prior art air conditioning ducting. A basic disadvantage of such approach, however, is that a large number of cutting tools of various sizes must be kept available in order to cut a hole which is sized properly for a specific duct fitting. Further, there can be difficulty in inserting a fitting into a hole cut for it, if the precut hole is irregular, or too small. If the hole is too large, the fitting will be loose and most likely it will be a source of undesirable air leakage.
Another problem encountered with the installation of branch duct fittings to main ducts of air conditioning systems, and the like, is that there must be found a manner of attaching the fitting to the duct. Other than the use of the aforementioned bent tabs, it is a common practice to employ bolts and similar fasteners which result in projection of the ends of the fasteners into the main duct. Such projections are generally quite undesirable, inasmuch as they cause turbulence in the air stream within the duct.
Accordingly, it is well known in the art to provide quick connection arrangements on duct fittings in order to eliminate the attachment problems referred to above, as well as to insure a good fit between the fitting and an associated duct. Examples of such quick connections can be found in U.S. Pat. No. 3,477,745 issued Nov. 11, 1969 to J. W. Williams et al and U.S. Pat. No. 3,915,477 issued Oct. 28, 1975 to D. R. Timmons. These fittings are intended specifically for use with reinforced fiberglass ducts and employ helical rings formed about the periphery of the connection end of the fitting, which permit the connection end of the fitting to be threaded through a precut hole. Once threaded through the duct, the split ring or flange retains the fitting in place on the duct.
With the latter approach, however, not only is it first necessary to precut a hole in the associated duct, the problems of which are discussed above, but also, during insertion of the fitting into the hole, the helical rings tend to tear or shred the wall in the area circumscribing the hole. This also is the case two, with U.S. Pat. No. 3,726,545 entitled "Air Duct Connector," which issued Apr. 10, 1973 to J. R. Grim et al. This latter patent discloses an air duct connector especially for use with reinforced fiberglass ducts in which the leading edge of the connector is provided with widely spaced cutting teeth for initially forming a circular aperture in the duct wall. Widely spaced radially extending tabs are provided proximate the cutting teeth for being threaded into the hole during cutting thereof to lock the fitting in the hole in the fiberglass duct or plenum chamber wall.
Besides tearing, or shredding the wall, a disadvantage of the construction suggested by Grim is that the cutting teeth, which are not intended to be bent over, will extend into the fluid flow path of the trunk duct so as to cause turbulence therein. Further, it is highly desirable to remove the cutout portion, or slug, of the duct wall from the interior of the duct, for such cutout portion could cause turbulence, air flow restriction, noise, and the like if left in the duct. In an instance in accordance with the Grim teaching, the workman concerned with the removal of the cutout portion must work very carefully through the mounting fitting in order to avoid being injured by the projecting cutting teeth.
Poorly fashioned cuts, such as result from the precutting of holes by the freehand use of a knife, razor blade, and the like, as required in some of the hereinbefore described prior art fittings, usually results in loose fits and highly undesirable air leakage. Over a period of months, this can amount to a serious amount of wastage. Also, sidewall tearing or shredding resulting from the use of other above discussed prior art fittings can result in leakage-prone weak spots in the areas where the fittings are mounted to the trunk duct. Furthermore, it is most important to keep shredded fibers out of the air moving in the duct system, to prevent the known health hazard associated with airborne fibers.
Regardless of the technique used to mount a branch line fitting in a main or trunk duct, a problem has long existed with regard to diverting air out of the airflow stream in the trunk duct into the branch duct. In many prior art systems, this air diversion problem is simply ignored, with the result being that the pressure of the air in the trunk duct will be totally relied upon to cause a suitable amount of air to move into the branch duct. In many instances, the failure to accomplish a dynamic redirecting of the air flowing in the trunk duct results in inadequate air flow in the branch lines.
The Goettel U.S. Pat. No. 4,491,124 entitled "Self-Tapping Duct Fitting," which issued Jan. 1, 1985, attempted to solve the air diversion problem by pivotally mounting a flat plate damper in the duct fitting and providing a suitable linkage so that subsequent to fitting installation, the damper could be moved to a fully open position wherein a relatively small portion of the flat plate extends from the fitting into the air stream of the trunk duct. While this improved the situation with regard to the abovediscussed air diversion problem, the air striking the flat plate damper was found to create considerable turbulence both in the trunk duct and in the branch duct, and acted as a restriction in those air streams. In addition, the relatively expensive damper, its mounting arrangement, and the needed linkage proved to be far too costly for the minimal results achieved therefrom.
The Goettel U.S. Pat. Nos. 4,491,124 and 4,569,110 are related to cutting tap-in orifices and tapping into rectangular ducts, rather than tapping into cylindrical ducts of flexible material, as taught by this invention. The Goettel patents represent a manifest relationship to the sheet-metal technology of the prior art, which is in distinct contrast to insulated spiral-tube flexible forms in combination with sheet-metal devices, as more recently developed.
The Nash U.S. Pat. No. 4,294,476 is also related to metal ductwork connections. The Harris U.S. Pat. No. 4,249,758 teaches joining a tubular member to a flat component such as a rectangular junction box or a sheet-metal duct.
The Wachter U.S. Pat. No. 4,147,382 entitled "Connecting Piece for a Branch Duct to a Substantially Round Air Conditioning Duct," describes the joining of cylindrical trunk tubes to cylindrical branch tubes, but in a somewhat different manner than earlier taught. The Wachter patent employs an elongate base on a branch tube that was connected to a trunk tube with a rectangular-to-cylindrical geometry rather than right-angle tubular-intersection joints.
The Grim et al U.S. Pat. No. 3,726,545 and the Primich et al U.S. Pat. No. 3,290,066, each previously mentioned, likewise taught joining of a circular branch member to a plenum chamber in the form of a junction box or flat-walled duct. Primich et al, Goettel and others have taught the use of tabs bendable to form a flange effect, but in a different form and relationship of parts than employed in this invention, as will be seen hereinafter. All of these prior patents relate to junctures with flat surfaces.
The Rice et al U.S. Pat. No. 4,491,349 entitled "Y-Connection for Flexible Conduit," which issued Jan. 1, 1985, is designed for use with a thin wall metal main conduit which has a plurality of grooves or corrugations extending around its periphery, "to provide the conduit with a degree of flexibility." The patentees describe that they utilize an inner shoe of sheet metal provided with a centrally disposed hole, as well as a saddle, with the inner shoe being intended to be inserted in through a hole several inches in diameter that is cut into the metal conduit that Rice et al are concerned with. The inner shoe is brought into a desired alignment with the hole in the conduit, with the tabs disposed around the periphery of the hole in the inner shoe being bent so as to extend upwardly through the hole in the metal conduit, and then pressed back against the outer face of the metal conduit. At this point the saddle with its short section of branch conduit is mounted over the hole in the metal conduit, in a desired relationship with the inner shoe. As described by the patentees Rice et al, rivets, spot welds or other suitable means are utilized to secure the tabs to the saddle.
It is important to note that both the internally positioned shoe and the externally positioned saddle utilized by Rice et al are stated to be dimensioned to extend around approximately 160.degree. of the periphery of the metal conduit. Quite clearly, the weight of such large and bulky components as suggested by Rice et al would not be suitable for use with highly flexible ducting, and Rice et al do not in any manner explain how their heavy devices could be attached in any suitable and appropriate manner to light-duty flexible ducting. Also, the use of the Rice et al technique requires the workman to have access to the end of the duct in order that the shoe can be inserted. As will be seen hereinafter, end access is not required for the installation of the novel duct fitting in accordance with this invention.
It is manifestly obvious that Rice et al are not dealing with attachment to the same type of highly flexible ducting as is involved in the present invention. As pointed out hereinabove, the wording set forth in the Rice et al patent describes that the patentees utilize a metal main conduit equipped with a plurality of grooves or corrugations that provide the conduit with "a degree of flexibility," but Rice et al make absolutely no mention of any use with the highly flexible ducting with which the present invention is principally intended for use. The flexible conduit with which Rice et al are concerned would be able to be bent only to a limited extent in order to be able to pass around an obstacle in the path of the ducting, and such conduit could not tolerate short radius turns, as could the highly flexible ducting being principally referred to in conjunction with the instant invention. Also, the flexible conduit utilized by Rice et al could not withstand without substantial damage, any partial collapse of the conduit sidewalls, amounting to a reduction in diameter. In distinct contrast, the highly flexible ducting with which the present invention is principally concerned could clearly be utilized in the situation in which the ducting is caused to pass through a narrow opening or passageway, for any reduction in the diameter would cause no intrinsic damage to the highly flexible ducting, for it would merely increase in diameter at a location 90.degree. to the location where the diameter has been reduced.
Another important point of distinction is that some 25 feet of the flexible metal conduit utilized by Rice et al could not possibly be compressed into a box approximately 30 inches long, as can the highly flexible ducting with which the instant invention is involved.
It is therefore most important to realize that the absence of effective devices and methods for joining round branch tubes to highly flexible trunk tubes in a desirable perpendicular relationship represents a distinct deficiency of all of these prior art devices. Quite unfortunately, the prior art has not taught an effective, efficient, low-cost and non-hazardous right-angle, direct joining of round branch air-conditioning/heating ducts to round, highly flexible ducts utilized as air-conditioning/heating trunks, as is taught by the instant invention.
It is an important goal of this invention to provide a new and highly improved duct fitting and method for mounting thereof which overcomes the problems and shortcomings of the prior art, and greatly improves the procedures for securing branch lines to trunk ducts made of highly flexible ducting.